1. Field of the Invention
The invention relates to routing multicast packets.
2. Related Art
In a network of networks, sometimes called an "internet" (alternatively, an "intranet"), routers are typically separated into a set of routing domains (alternatively, "autonomous routing groups" or "domains"). Routers in each routing domain maintain information about destinations and associated "next hops" to those destinations; the routers are able to maintain such information by exchanging routing protocol messages.
Such networks can include systems for transmitting packets which are unicast (directed to a single destination device) or multicast (directed to multiple destination devices). When packets are multicast, they are transmitted using a multicast distribution tree. Accordingly, when a router forwards a multicast packet, the router must maintain routing information about its communication interface to the next hop toward the root of the multicast distribution tree, and for all successive next hops leading to the multiple destination devices.
One problem which has arisen in the art is that a large amount of information must therefore be recorded for routing multicast packets; this problem is made worse with increasing size of the internet.
Accordingly, it would be desirable to provide a method and system for routing multicast packets in an internet, in which not all routers in a routing domain would be required to maintain complete routing information for roots of multicast trees, if those roots are external to the routing domain. This advantage is achieved in an embodiment of the invention in which only selected routers in a routing domain maintain routing information about those roots which are external to the routing domain, while all other routers in the routing domain maintain only routing information about those roots which are internal to the routing domain.